JPH0736231B2 - Optical head - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical head in an optical disk device.

(Prior Art) An optical disk device is a device that records information on an optical disk according to a command from a computer or the like, and reads and reproduces the recorded information. A drive device that rotates a disc-shaped optical disk, an optical head , And these control devices and the like.

Generally, in this type of optical disk device, a laser light beam such as a semiconductor laser is focused on the optical disk and a fine track (for example, a gap of about 1.6 μm) is scanned to record information on the track, or The operation of reading the information of is performed. Therefore, in the optical head, focus control (focus control) that keeps the light beam in an appropriate focused state (for example, spot diameter 1 μm), track control that keeps the focused spot from being out of the track, and access to search for a desired track are performed. It has three functions of control.

Conventionally, as a technique in such a field, JP-A-59-1935
It was described in Japanese Patent Laid-Open No. 53. The configuration will be described below with reference to the drawings.

FIG. 2 is a configuration diagram showing a configuration example of a conventional optical head.

In the figure, a disk-shaped optical disc 1, a head actuator 2, and an optical head 3 are shown. The optical head 3 is arranged so as to face the surface of the optical disk 1, and has a structure that can be moved in the radial direction (radial direction) of the optical disk 1 by the head actuator 2.

The optical head 3 comprises a light source 5, which is a semiconductor laser, a polarization beam splitter 6, a beam splitter 7, an objective lens 8, a prism 9, a half mirror 10, on a head base 4.
A focus error detector 11, a tracking position detector 12, a lens position detector 13, a focus actuator 14, a tracking actuator 15 and the like are mounted. Objective lens 8
Is movable in a direction substantially perpendicular to the surface of the optical disk 1 (direction of arrow Y), and the beam splitter 7 and the prism 9 including the objective lens 8 thereof are movable in the radial direction of surface 1 of the optical disk (direction of arrow X). Is mounted on the head base 4. The focus actuator 14 gives a driving force in the arrow Y direction, and the tracking actuator 15 gives a driving force in the arrow X direction.

In the above configuration, the light beam projected from the light source 4 reaches the beam splitter 7 through the splitter 6,
After the optical path is changed by the beam splitter 7, the light is incident on the surface of the optical disc 1 through the objective lens 8. The reflected light from the surface of the optical disk 1 reaches the beam splitter 7 through the objective lens 8 and is reflected by the beam splitter 7 in two directions. One of the reflected lights undergoes optical path conversion by the prism 9 and then enters the lens position detector 13, and the other reflected light undergoes optical path conversion by the polarization beam splitter 6 and the Har mirror 10 and then the focus error detector 11 and tracking. It is incident on the position detector 12.

The focus error detector 11 performs focus error detection together with a control circuit (not shown), operates the focus actuator 14 by the focus error signal, and moves only the objective lens 8 in the arrow Y direction to perform focus control.

The tracking position detector 12 detects a tracking position error together with a control circuit (not shown), and a tracking actuator is detected by the tracking position error signal.
15 is operated to move the beam splitter 7, the objective lens 8 and the prism 9 in the arrow X direction to perform track control.

Further, in order to perform access control, the beam splitter 7, the objective lens 8 and the prism 9 are fixed at predetermined positions in the arrow X direction based on the detection signal of the lens position detector 13, and then the head actuator 2 is operated to activate the optical head. The whole 3 is moved in the radial direction of the optical disc 1 at high speed to perform rough positioning. After that, the tracking actuator 15 is operated to perform precise positioning in the direction of the arrow X to complete the access control.

In this type of optical head, a beam splitter 7 including an objective lens 8 and a prism 9 at a fixed position of the head base 4.
Since the optical head 3 is moved at a high speed in the radial direction of the optical disc 1 with the position fixed, the unnecessary vibration in the radial direction of the optical disc with respect to the objective lens 8 can be suppressed and a desired track can be accessed at high speed.

(Problems to be Solved by the Invention) However, in the optical head having the above-described configuration, since access control is performed by moving the entire optical head 3, it is difficult to perform accurate and high-speed access due to the weight of the optical head 3. Therefore, in order to increase the access speed, it is necessary to increase the size of the head actuator 2 and increase its driving force. Further, in order to suppress the vibration of the objective lens 8 in the radial direction of the optical disc, a lens position detector 13 and a control circuit for fixing the objective lens 8 at a fixed position based on the detection signal are required, which complicates the control system. There was a problem that

DISCLOSURE OF THE INVENTION The present invention has the problems that the above-mentioned prior art has the problems that it is difficult to access the optical head with high precision at high speed without increasing the moving mechanism of the optical head, and a special control system for suppressing vibration. It is an object of the present invention to provide an optical head that solves the need for.

(Means for Solving Problems) In order to solve the above problems, the present invention relates to an optical head of an optical disk device for reproducing or recording information on an optical disk, wherein a light beam to be irradiated onto the optical disk surface. A fixedly arranged optical system for projecting light and receiving reflected light from the optical disk surface, a fixedly arranged magnetic circuit member including a magnet and a yoke member, a fixedly arranged guide member, the light beam, and A carriage having an optical path exchanging means for changing the optical path of the reflected light and slidably supported by the guide member in the radial direction of the optical disc surface, an objective lens and a control coil, and substantially the optical disc surface. And an objective lens holder engaged with the carriage slidably in the vertical direction.

Here, the objective lens is arranged between the optical disc surface and the optical path changing means, irradiates the optical beam from the optical path exchanging means onto the optical disc surface, and receives reflected light from the optical disc surface. It is a lens that does. The control coil is a coil that cooperates with the magnetic circuit member to generate an electromagnetic force. The optical path changing means is arranged such that the optical path changing point around the optical axis of the light beam is separated from the neutral point position of the operation of the objective lens by approximately twice the focal length of the objective lens.

(Operation) According to the present invention, since the optical head is configured as described above, when a current flows in the control coil, the objective lens holder is moved by the electromagnetic force in the radial direction of the optical disc through the carriage and the direction substantially perpendicular thereto. Work to move. The light beam emitted from the optical system is converged on the optical disk surface by the objective lens after the optical path is changed by the optical path changing means provided on the carriage. Then, the reflected light from the optical disk surface returns to the optical system after the optical path is changed by the optical path changing means through the objective lens. At this time, in the optical path changing means provided in the carriage, since the optical path changing point at the center of the optical axis of the light beam is apart from the operation neutral point position of the objective lens by approximately twice the focal length of the objective lens, Works to remove the optical axis shift of the reflected light due to the inclination of. This enables highly accurate and high speed access.
Therefore, the above problems can be eliminated.

(Embodiment) FIG. 1 is a perspective view of an essential part of an optical head showing an embodiment of the present invention, and FIG. 3 is a sectional view taken along line I-I of FIG.

This optical head is arranged so as to face the optical disc 1, and an optical system 20 is fixedly arranged on the outer periphery of the optical disc 1. The optical system 20 includes a semiconductor laser, a focus / track error detector, a signal detector, and the like.

Further, a pair of magnetic circuit members 21-1 and 21-2 are fixedly arranged in the radial direction of the optical disc 1. One of the magnetic circuit members 21-1 is a plate-shaped magnet 22-1 arranged in the radial direction of the optical disk 1 and yoke members 23-1, 24- that surround the magnet 22-1 and form a closed magnetic path. 1 and a magnetic gap 25-1 formed between the magnet 22-1 and the yoke member 24-1.
It consists of and. Similarly, other magnetic circuit members
2 also includes a plate-shaped magnet 22-2, yoke members 23-2 and 24-2, and a magnetic gap 25-2. The optical system 20 and the magnetic circuit members 21-1 and 21-2 are fixed to a frame (not shown). In addition, a pair of rod-shaped guide members 26-1 and 26-2 are fixedly arranged substantially parallel to the magnets 22-1 and 22-2.

An objective lens holder 30 is mounted on the opposing yoke members 24-1 and 24-2 so as to straddle them. A cylindrical tubular member 31 is provided substantially in the center of the objective lens holder 30 in a direction substantially perpendicular to the surface of the optical disc 1, and the tubular member 31 is provided.
An objective lens 32 is attached to one end of the cylindrical lens, and a hole 33 for passing a light beam is provided in a part of the cylindrical member 31. Further, the focus control coil 34 and the track control coils 35-1 and 35-2 are wound around the outer peripheral surface of the objective lens holder 30 so as to be substantially orthogonal to each other in the magnetic gaps 25-1 and 25-2.

A carriage 40 that engages with the objective lens holder 30 is provided at a position adjacent to the objective lens holder 30. The carriage 40 has a movable base 41 slidably supported by a pair of guide members 26-1 and 26-2 via sliding bearings and the like, and a cylindrical member 31 slidably provided on the movable base 41 so as to project. And a cylindrical tubular body 42 inserted into the. Furthermore, an objective lens holder is mounted on the movable table 41.
A pin 43 is attached to prevent rotation of 30 and
A hole 44 for passing a light beam is formed in 42. Further, an optical path changing means, for example, a mirror (mirror surface body) 45 is attached in the cylindrical body 42 at an angle of about 45 ° with respect to the surface of the optical disc 1. The mirror 45 has a reflecting surface that reflects the center of the optical axis of the light beam from the optical system 20 and is placed away from the neutral position of the movement of the objective lens 32 by a distance approximately twice the focal length of the objective lens 32. Has been done.

Next, the operation will be described.

(1) Focus control The parallel light beam emitted from the optical system 20 has a hole 33 in the objective lens holder 30 as shown by broken lines in FIGS. 1 and 3.
Then, the light passes through the hole 44 of the carriage 40, is reflected at a right angle by the mirror 45, and is converged on the recording surface of the optical disc 1 by the objective lens 32. On the other hand, the reflected light from the optical disc 1 returns to the optical system 20 via the objective lens 32 and the mirror 45, and the focus / track error and the signal are detected.

When a focus error is detected by the optical system 20, a current flows through the focus control coil 34 by a control circuit (not shown) based on this focus error signal. The objective lens holder 30 receives the electromagnetic force due to the action of the current flowing through the focus control coil 34 and the magnetic field in the magnetic gaps 25-1, 25-2 in the magnetic circuit members 21-1, 21-2, and the objective lens holder 30 is a cylinder of the carriage 40. It moves up and down along the body 42. That is, when the focus control coil 34 is energized in the direction of arrow a in FIG. 1, the objective lens holder 30 moves upward, and when energized in the direction of arrow b, the objective lens holder 30 moves downward. To do.

In this way, the energizing direction for the focus control coil 34,
Further, by controlling the energizing current value or energizing time, the objective lens 32 approaches or moves away from the optical disc 1, and a predetermined focus control is performed.

(2) Track control When a track error is detected, based on this track error signal, a track control coil 35
Currents flow in the same direction in -1, 35-2. Current flowing in the track control coils 35-1, 35-2 and magnetic gap
Electromagnetic force is received by the action with the magnetic field in 25-1, 25-2,
The objective lens holder 30 includes the carriage 40 and the guide member 26.
Move along -1,26-2. That is, when the track control coils 35-1 and 35-2 are energized in the direction of arrow c in FIG. 1, the objective lens holder 30 and the carriage 40 move in the direction of arrow e, and when energized in the direction of arrow d. The objective lens holder 30 and the carriage 40 move in the direction of arrow f.

In this way, the objective lens 32 is moved in the radial direction of the optical disc 1 together with the mirror 45 by controlling the energization direction, the energization current value, or the energization time with respect to the track control coils 35-1 and 35-2. , Predetermined track control is performed.

(3) Access control In access control, the track control coil 35 is controlled by a control circuit (not shown) based on the difference between the designated position and the current position.
Current flows to -1,35-2. Track control coil 35-1,
An electromagnetic force is received by the action of the current flowing in 35-2 and the magnetic field in the magnetic gaps 25-1, 25-2, and the objective lens 32 along with the mirror 45 is moved in the radial direction of the optical disc 1 as in the track control. Access control is performed by moving. As these position detecting means, the number of tracks crossed may be counted, or an external scale or the like may be used.

The focus control and the track control described above are simultaneously performed in a combined manner as needed, but when the access control is performed, the track control is once turned off and the objective lens 32
Are turned on again after moving by the desired amount.

(4) The problem of the deviation of the optical axis of the reflected light due to the parallel error between the light beam and the guide members 26-1 and 26-2.

When the optical system 20 is fixed and the objective lens 32 and the mirror 45 are scanned in the radial direction over the entire track of the optical disc 1, the optical axis of the light beam emitted from the optical system 20 and the mirror 45.
If there is an inclination with the moving axis of the optical disc 1 (that is, the axes of the guide members 26-1 and 26-2), the optical axis of the reflected light from the optical disc 1 is shifted.

For example, as shown in FIG. 4, when the moving axis of the mirror 45 and the optical axis A of the light beam are inclined by the angle α radian, the reflected optical axis from the optical disc 1 is B at the first position X1. When the mirror 45 and the objective lens 32 move to the second position X2 which is separated from the first position X1 by the distance L1, the reflected optical axis from the optical disc 1 becomes C, and the reflected optical axis is the distance d1 (= 2L1.
Only α) will move.

The movement of the reflected optical axis from the optical disc 1 causes an offset in the output of the track error detector in the optical system 20,
Track deviation occurs. According to the experimental results, when L = 30 mm, it is necessary to adjust the angle α to 5 milliradians or less in order to maintain the desired track following accuracy. Therefore, it is desirable to set the angle α to 5 milliradians or less in advance, or to provide the optical system 20, the guide members 26-1, 26-2, etc. with an adjusting mechanism so that the angle α can be finely adjusted. .

(5) The problem of the optical axis shift of the reflected light due to the inclination of the carriage 40.

The deviation of the reflected optical axis from the optical disk 20 is caused by the guide member 26-
Sleds, bends, or guide members 26-1, 26-2
This also occurs when the carriage 40 is tilted due to the rattling of -2 and the moving base 41.

For example, as shown in FIG. 5, the carriage 40 is tilted by an angle β radian, so that the objective lens 32 and the mirror 45 are tilted by an angle β.
When tilted in radians, the reflected optical axis moves a distance d2.

Here, if the focal length of the objective lens 32 is F and the distance between the objective lens 32 and the reflecting surface of the mirror 45 is L2, then d2 = 2 (L2−2F) · β. In this formula, if L2 = 2F is set, d2 = 0
Becomes Since the objective lens 32 moves up and down by focus control, the value of the distance L2 also changes, but the distance between the neutral point of operation of the objective lens 32 and the reflecting surface of the mirror 45 is 2F.
By setting, the deviation of the reflected optical axis from the optical disc 1 becomes a practically negligible value.

The advantages of this embodiment can be summarized as follows.

The focus control magnetic circuit and the track access control magnetic circuit are commonly used, and those magnetic circuit members are used.
Since 21-1 and 21-2 are fixed to the outside of the movable part, the weight of the movable part is lightened, high-speed access is possible, and high-speed followability of track control can be secured.

Since the optical head of the present embodiment is configured to directly drive the objective lens 32, the objective lens 32 can be used even during high-speed access.
It is possible to accurately search a desired track without the 32 vibrating.

Move the mirror 45 approximately 2F from the neutral position of the objective lens 32.
The distance between the optical system 20 and the guide members 26-1 and 26-2 is adjusted to, for example, 5 milliradians or less to maintain desired tracking accuracy over the entire track of the optical disc 1. It becomes possible.

The present invention is not limited to the illustrated embodiment, and the entire structure of the optical head can be variously modified. For example, a guide member
26-1 and 26-2 are rail-shaped, or a tubular member 31 and a tubular body.
The pin 43 may be omitted by forming 42 into a rectangular tube shape.

(Effects of the Invention) As described in detail above, according to the present invention, since the objective lens is directly driven by the control coil, the weight of the movable portion is reduced, and high-speed access is possible.
In addition, high-speed followability of track control can be secured. Moreover, without using complicated vibration control means as in the past,
It is possible to accurately search for a desired track without vibrating the objective lens during high-speed access.

Further, since the optical path changing point of the optical axis of the light beam in the optical path changing means is arranged at a distance of approximately twice the focal length of the objective lens from the operation neutral point position of the objective lens, even if the carriage is tilted. The deviation of the optical axis reflected from the optical disk can be eliminated or can be set to a negligibly small value, and the desired tracking accuracy can be maintained over the entire track of the optical disk.

[Brief description of drawings]

FIG. 1 is a perspective view of an essential part of an optical head showing an embodiment of the present invention, FIG. 2 is a structural view of a conventional optical head, and FIG.
FIG. 4 is a sectional view taken along line I-I of FIG. 4, and FIGS. 1 ... Optical disc, 20 ... Optical system, 21-1, 21-2 ... Magnetic circuit member, 22-1, 22-2 ... Magnet, 23-1, 23-2, 24--
1, 24-2 ... Yoke member, 25-1, 25-2 ... Magnetic gap, 26-1, 26-2 ... Guide member, 30 ... Objective lens holder, 32 ... Objective lens, 34, 35 -1,35-2 ... Control coil, 40 ... Carriage, 45 ... Optical path changing means.

Claims (1)

[Claims] 1. A fixed arrangement for projecting a light beam to be irradiated onto the optical disk surface and receiving reflected light from the optical disk surface in an optical head of an optical disk device for reproducing or recording information on the optical disk. The optical system, a fixed magnetic circuit member including a magnet and a yoke member, a fixed guide member, and an optical path exchanging means for changing the optical paths of the light beam and the reflected light. A carriage, which is slidably supported in the radial direction by the guide member, is disposed between the optical disk surface and the optical path exchanging means, irradiates the optical beam from the optical path exchanging means onto the optical disk surface, and The optical disk surface includes an objective lens that receives reflected light from the optical disk surface, and a control coil that cooperates with the magnetic circuit member to generate an electromagnetic force. And an objective lens holder that is slidably engaged in the carriage in a substantially vertical direction, and an optical path changing point of the optical beam optical axis center in the optical path exchanging means from an operation neutral point position of the objective lens. An optical head, which is arranged at a distance of about twice the focal length of the objective lens.